Overview

One of the core forces behind object-oriented development is the need to manage increasing application complexity. Object-oriented techniques are not a magic bullet in this regard; however, a well-executed object-oriented design will result in well-partitioned assignment of responsibility across the objects within the design--a major step toward isolating complex pieces of an application.Many of you have already discovered the power of object-oriented design patterns when defining and implementing complex applications. IBM's SanFrancisco Application Business Components is a set of frameworks that have been built around design patterns, both those that are well known throughout the software industry and new patterns described in this book. Why new design patterns? As we analyzed the requirements of typical business applications, we discovered many recurring situations whose needs were not adequately met by existing patterns. Often those needs could be met by extensions of well-known patterns; sometimes new patterns arose directly out of specific business application requirements. This book covers both the extended and the new patterns of IBM SanFrancisco, describing them within the context of a typical business application's requirements.So what should you expect to get out of this book? The design patterns documented here capture the experiences we have gained from developing business components across multiple business domains. Every pattern in this book has been refined through multiple uses within SanFrancisco and has been validated by users of the frameworks as they build and deploy applications based on SanFrancisco. In particular, we have found these patterns very useful in helping us "think outside of the box" when confronted with complex business application requirements.Regardless of your level of design experience, we encourage you to read this book with an eye toward the design problems you have come across in your past and toward opportunities to apply these patterns (or extensions of them) to your current projects.About This BookThis book follows the format established by Gamma, Vlissides, Johnson, and Helm (the "Gang of Four") in their groundbreaking book Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley, 1995). Beginning in Chapter 2 with a case study describing a typical set of business requirements for a hypothetical food distribution enterprise, the book continues with chapters that address each design pattern in turn. Each pattern is defined along the lines of the standard design pattern template used by the Design Patterns book, typically incorporating an aspect of the case study to provide a concrete example that motivates the pattern.IntroductionOver the course of IBM SanFrancisco development, our belief in design patterns as a core component of effective object-oriented development has been strongly reinforced. Chapter 1 distills some of the key reasons for this belief. Those of you who are already sold on design patterns won't find any great revelations here, but we hope you will find the consolidation of these points in one place to be useful. Those of you who are new to design patterns will find some strong arguments for using them in all your object-oriented development projects.Case StudyDesign patterns don't exist in a vacuum. Each design pattern described in this book was developed as a result of meeting real-life business application requirements. What we have attempted to do in the case study (Chapter 2) is provide a business context for many of the patterns in this book. (Although not all patterns are used in the case study, we provide a detailed business motivation in each pattern chapter of this book.) If your background is oriented toward business analysis, the case study will help justify these patterns and will help you make the leap from business domain analysis to object-oriented design. If your background is primarily technical, the case study will help you communicate with business experts as you jointly explore the right solutions for specific application requirements.Design PatternsDesign patterns, as you would expect, are the core of this book. Many of the design patterns we describe build on or are extensions of patterns defined in Design Patterns, and you will find it helpful to have previously read about and used those patterns. However, each pattern in this book is described in enough detail for you to understand its purpose, design, and implementation without a detailed knowledge of any underlying design patterns.This book divides the patterns into five major categories:Part I: Foundational Patterns. SanFrancisco's foundational patterns provide an underlying structure for all SanFrancisco-based business objects. The foundational patterns provide mechanisms for business object creation, changing behavior, and construction of business processes. Many of these patterns are incorporated into higher-level patterns described in the remaining parts of the book. Part II: Behavioral Patterns. SanFrancisco's behavioral patterns describe various methods of incorporating flexible algorithms throughout a business application. Each of the behavioral object patterns described in this book defines a variation or extension of the Strategy pattern defined by Design Patterns. Part III: Structural Patterns. SanFrancisco's structural patterns are concerned with how business information is organized and accessed. Structural class patterns deal with the issue of business information access through inheritance. Structural object patterns define how business information (in the form of business objects) is organized within the scope of a complex business environment. Part IV: Process Patterns. SanFrancisco's process patterns are concerned with how businesses organize and process information. The process patterns do not identify the information involved, but rather define how businesses work with that information. Process patterns can be applied in many business situations. The use of these patterns provides consistency for the same types of processes, allowing the user to grasp more quickly the mode of information processing and the flexibility provided as part of that processing. Part V: Dynamic Behavioral Patterns. SanFrancisco's dynamic behavioral patterns describe object-oriented approaches for modeling entities in the business domain that exhibit behavioral changes throughout their existence--not only changes to existing behavior, but also changes to the set of behaviors (responsibilities) supported by the business entity at any given time. The dynamic behavioral patterns described in this book build on the general concepts described in the State pattern of Design Patterns and on one another.0201616440P04062001